Interferons(IFNs) exhibit an antiproliferative effect on many normal and transformed cells and have in vivo antitumor activity in a variety of cancers. Recent clinical studies have suggested major activity with IFNs, especially in advanced squamous cell carcinoma of the skin and cervix. With the objective of exploring how the IFNs might work in squamous carcinoma cell line, we studied the effect of IFN-a on cervical cancer cell lines. The effect of IFNs on apoptosis and cell cycle of cervical cancer cell lines(C33A, CaSki, SiHa, HeLa, ME-180) was analysed by flow cytometry in time dependent manner. Results were as follows: (1) According to cell count of studied cancer cell lines treated with 2,000 IU/ml IFN-a for 7 days exposure, IFN-a had the antiproliferative effect on all five tested cervical cancer cell lines. Also this antiproliferative effect was confirmed by WST-1 assay. (2) The effect of IFN-a on apoptosis of each cultute was analysed by flow cytometry after 3 days and 7 days exposure with 2,000 IU/ml IFN-a, Apoptosis was not induced by IFN-a treatment. (3) The effect of IFN-a on the cell cycle of each culture was analysed by flow cytometry after 3 days exposure with 2,000 IU/ml IFN-a. As compared to control cells, treatment with IFN-a resulted in a higher proportion of cells in S phase with lower portion of cells with G2/M phase. (4) Time course of IFN-a effect on HPV 16 and HPV 18 E6 mRNA levels was evaluated by northern blot analysis. In CaSki cell line, HPV 16 E6 mRNA expression induced by IFN-a was not inhibited. But in HeLa cell line, HPV 18 E6 inRNA expression was inhibited. IFN-a appears to have the antiproliferative effect on all five tested cervical cancer cell lines and the antiproliferative effect of IFN-a seemed to be induced not by apoptosis but by disruption on specific cell cycle. Also regulation of HPV E6 mRNA expression induced by IFN-a is not directly related to the mechanisms of the antiproliferative effect of IFN-a in cancer cell lines.